Fibrous non-woven materials and fibrous non-woven composite materials are widely used as products, or as components of products, such as wet-wipes because they can be manufactured inexpensively and made to have specific characteristics. These products can be manufactured so inexpensively that they can be viewed as disposable, as opposed to reusable.
One approach to making fibrous non-woven composite materials for wet-wipes is the use of homogeneous mixtures of materials such as air laid webs of fibers mixed with cellulosic fibers or another absorbent material. Other wet-wipes have been prepared by joining different types of non-woven materials in a laminate or formed as a layered structure. These products can be prepared from plastic materials such as plastic sheets, films and non-woven webs, prepared by extrusion processes such as, for example, slot film extrusion, blown bubble film extrusion, meltblowing of non-woven webs and spinbonding.
The non-woven materials and laminated non-woven materials that are useful for consumer products should meet minimum product standards for strength, moisture level, size, flexibility, thickness, softness and texture. However, if one of these parameters is changed this can affect another of the parameters. Thus, a goal for these laminates is to produce a product that can mimic a soft cloth-like feel or at least get closer to a soft cloth-like feel than has been previously possible while still maintaining acceptable strength.
Such a soft cloth-like feel is often characterized by, among other things, one or more of the following: thickness, bulk density, flexibility, texture, softness, density, and durability of the non-woven materials. These materials are suitable for disposable products such as, for example, disposable diapers, disposable tissues and disposable wipes, for example, disposable wet wipes.
Producing a high quality composite elastic material or Stretch Bonded Laminate (SBL) at a low cost can be difficult. Often the polymers having high elasticity are expensive. It would be advantageous to have a method to provide a high quality SBL and maintain a low cost. In addition it would be advantageous to have a method for controlling the amount of retraction of the SBL. The ability to control the retraction can provide a product having less variability in attributes like basis weight, thickness, stretch to stop, and percent retraction.
For the purposes of the present application, the following terms shall have the following meanings:
The term xe2x80x9celasticxe2x80x9d as used herein, means any material which, upon application of a biasing force, is stretchable, that is, elongatable at least about 60 percent (i.e., to a stretched, biased length which is at least about 160 percent of its relaxed unbiased length), and which, can recover at least 55 percent of its elongation upon release of the stretching, elongating force. A hypothetical example would be a one (1) cm sample of a material which is elongatable to at least 1.60 cm and which, upon being elongated to 1.60 cm and released, can recover to a length of not more than 1.27 cm. Many elastic materials can be elongated by much more than 60 percent (i.e., much more than 160 percent of their relaxed length), for example, elongated 100 percent or more, and many of these can recover to substantially their initial relaxed length, for example, to within 105 percent of their original relaxed length, upon release of the stretching force.
As used herein, the term xe2x80x9cnon-elasticxe2x80x9d refers to any material which does not fall within the definition of xe2x80x9celastic,xe2x80x9d above.
As used herein the term xe2x80x9cnon-woven webxe2x80x9d means a structure or a web of material which has been formed without use of weaving processes to produce a structure of individual fibers or threads which are intermeshed, but not in an identifiable, repeating manner. Non-woven webs have been, in the past, formed by a variety of conventional processes such as, for example, meltblowing processes, spinbonding processes, film aperturing processes and staple fiber carding processes.
The terms xe2x80x9crecoverxe2x80x9d and xe2x80x9crecoveryxe2x80x9d as used herein refer to a contraction of a stretched material upon termination of a biasing force following stretching of the material by application of the biasing force. For example, if a material having a relaxed, unbiased length of one (1) cm is elongated 50 percent by stretching to a length of one and one half (1.5) cm the material would be elongated 50 percent (0.5 cm) and would have a stretched length that is 150 percent of its relaxed length. If this exemplary stretched material contracted, that is recovered to a length of one and one tenth (1.1) cm after release of the biasing and stretching force, the material would have recovered 80 percent (0.4 cm) of its one-half (0.5) cm elongation. Recovery can be expressed as [(maximum stretch lengthxe2x80x94final sample length)/(maximum stretch lengthxe2x80x94initial sample length)] times 100.
As used herein, the term xe2x80x9cmeltblown fibersxe2x80x9d means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into a high velocity gas (e.g. air) stream which attenuates the filaments of molten thermoplastic material to reduce their diameter, which can be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin.
As used herein, the term xe2x80x9cspunbonded fibersxe2x80x9d refers to small diameter fibers which are formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries of a spinnerette with the diameter of the extruded filaments then being rapidly reduced as by, for example, eductive drawing or other well-known spun-bonding mechanisms. The production of spun-bonded non-woven webs is illustrated in patents such as, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al.
As used herein, the term xe2x80x9ccoformxe2x80x9d means a non-woven composite material of air-formed matrix material comprising thermoplastic polymeric meltblown fibers such as, for example, microfibers having an average fiber diameter of less than about 10 microns, and a multiplicity of individualized absorbent fibers such as, for example, wood pulp fibers disposed throughout the matrix of polymer microfibers and engaging at least some of the micro fibers to space the microfibers apart from each other. The absorbent fibers are interconnected by and held captive within the matrix of microfibers by mechanical entanglement of the microfibers with the absorbent fibers, the mechanical entanglement and interconnection of the microfibers and absorbent fibers alone forming a coherent integrated fibrous structure. These materials are prepared according to the descriptions in U.S. Pat. No. 4,100,324 to Anderson et al. U.S. Pat. No. 5,508,102 to Georger et al. and U.S. Pat. No. 5,385,775 to Wright.
As used herein, the term xe2x80x9cmicrofibersxe2x80x9d means small diameter fibers having an average diameter not greater than about 100 microns, for example, having an average diameter of from about 0.5 microns to about 50 microns, or more particularly, microfibers may have an average diameter of from about 4 microns to about 40 microns.
As used herein, the term xe2x80x9cautogenous bondingxe2x80x9d means bonding provided by fusion and/or self-adhesion of fibers and/or filaments without an applied external adhesive or bonding agent. Autogenous bonding can be provided by contact between fibers and/or filaments while at least a portion of the fibers and/or filaments are semi-molten or tacky. Autogenous bonding may also be provided by blending a tackifying resin with the thermoplastic polymers used to form the fibers and/or filaments. Fibers and/or filaments formed from such a blend can be adapted to self-bond with or without the application of pressure and/or heat. Solvents may also be used to cause fusion of fibers and filaments which remains after the solvent is removed.
As used herein, the term xe2x80x9cmachine direction (MD)xe2x80x9d refers to the direction of travel of the forming surface onto which fibers are deposited during formation of a non-woven fibrous web.
As used herein, the term xe2x80x9ccross-machine direction (CD)xe2x80x9d refers to the direction which is essentially perpendicular to the machine direction defined above.
As used herein, the term xe2x80x9ctensile strengthxe2x80x9d refers to the maximum load or force (i.e., peak load) encountered while elongating the sample to break. Measurements of peak load are made in the machine and cross-machine directions using wet samples.
As used herein, the term xe2x80x9cwet wipexe2x80x9d refers to a fibrous sheet which, during its manufacture, has a liquid applied thereto so that the liquid can be retained on or within the fibrous sheet until its utilization by a consumer. The liquid may include a fragrance and/or an emollient and may serve to aid the fibrous sheet in retention of materials which are to be wiped up during its utilization.
As used herein, the terms xe2x80x9cstretch-bonded laminate (SBL)xe2x80x9d or xe2x80x9ccomposite elastic materialxe2x80x9d refers to a non-woven fabric including at least one layer of non-woven, elastic material and at least one layer of non-woven, non-elastic material, e.g., a gatherable layer. The SBLs of the invention include materials with combinations of layers that include at least one elastic web layer and at least one non-elastic web layer, e.g., an elastic layer between two gatherable layers. The elastic non-woven web layer(s) are joined or bonded in at least two locations to the non-elastic non-woven web layer(s). Preferably, the bonding is at intermittent bonding points or areas while the non-woven web layer(s) are in juxtaposed configuration and while the elastic non-woven web layer(s) have a tensioning force applied thereto in order to bring the elastic non-woven web to a stretched condition. Upon removal of the tensioning force after joining of the web layers, an elastic non-woven web layer will attempt to recover to its unstretched condition and will thereby gather the non-elastic non-woven web layer between the points or areas of joining of the two layers. The composite material is elastic in the direction of stretching of the elastic layer during joining of the layers and can be stretched until the gathers of the non-elastic non-woven web or film layer have been removed. A stretch-bonded laminate may include more than two layers. For example, the elastic non-woven web or film may have a non-elastic non-woven web layer joined to both of its sides while it is in a stretched condition so that a three layer non-woven web composite is formed having the structure of gathered non-elastic (non-woven web or film)/elastic (non-woven web or film)/gathered non-elastic (non-woven web or film). Yet other combinations of elastic and non-elastic layers can also be utilized. Such composite elastic materials are disclosed, for example, by U.S. Pat. No. 4,720,415 to Vander Wielen et al., and U.S. Pat. No. 5,385,775 to Wright.
As used herein xe2x80x9cthermal point bondingxe2x80x9d involves passing a material such as two or more webs of fibers to be bonded between a heated calender roll and an anvil roll. The calender roll is usually, though not always, patterned in some way so that the entire fabric is not bonded across its entire surface, and the anvil roll is usually flat. As a result, various patterns for calender rolls have been developed for functional as well as aesthetic reasons. In one embodiment of this invention the bond pattern allows void spaces in the machine direction to allow a gatherable layer to gather when the web retracts.
As used herein the term xe2x80x9csuperabsorbentxe2x80x9d refers to a water swellable, substantially insoluble organic or inorganic material capable of absorbing at least 10 times its weight of an aqueous solution containing 0.9 wt % of sodium chloride.
As used herein the term xe2x80x9cpalindromicxe2x80x9d means a multilayer laminate, for example a stretch-bonded laminate, which is substantially symmetrical. Examples of palindromic laminates could have layer configurations of A/B/A, A/B/B/A, A/A/B/B/A/A, A/B/C/B/A, and the like. Examples of non-palindromic layer configurations would include A/B/C, A/B/C/A, A/B/C/D, etc.
As used herein the term xe2x80x9cpolymerxe2x80x9d generally includes, but is not limited to, homopolymers, copolymers, such as, for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term xe2x80x9cpolymerxe2x80x9d shall include all possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic and random symmetries.
The present invention provides a method for increasing the amount of retraction in a composite elastic material or Stretch Bonded Laminate (SBL). The SBL can be heat activated to provide a means of increasing the amount of retraction of a composite elastic material or SBL fabric. The ability to increase the amount of retraction can provide a cost savings in producing the desired fabric qualities. This cost savings in producing the laminate is because the product produced will have the ability to stretch and retract more after heat activation in-line and allow the use of lower amounts of material in the stretchable layer.
In another aspect the heat activation can provide a method for controlling the amount of retraction. The ability to control the retraction can provide a product having less variability in attributes like basis weight, thickness, stretch to stop, and percent retraction.
The problem of lack of softness or cloth-like feel associated with previous composite elastic materials has been addressed by the composite elastic material of the present invention, which is adapted to provide a more cloth like feel than otherwise available. This can be accomplished by providing a non-woven composite material or SBL having a low cup crush (i.e., increased flexibility) and a low density (i.e., maximum bulk per unit mass), while maintaining a desired level of strength and tear resistance (i.e., sufficient tensile strength in both machine direction, MD, and in cross-machine direction, CD).
The composite elastic material of the present invention contains at least one elastic layer including a non-woven layer, optionally having embedded elastic fibers and at least one gatherable layer joined at spaced apart locations to the elastic layer so that the gatherable layer is gathered between the spaced-apart locations. The fibers of the gatherable and the elastic layer s extend generally in the MD and not in the CD.
The gatherable layer can be a non-woven web of fibers, such as, for example, spunbonded webs, meltblown webs, air laid layer webs, bonded carded webs, hydroentangled webs, wet-formed (wet laid) webs or any combination thereof. The gatherable layer may also be a mixture of fibers and one or more other materials such as, for example, wood pulp, staple-length fibers, particulates and super-absorbent materials. Such mixtures can be formed by adding fibers and/or particulates to the gas stream in which meltblown fibers are carried so that an intimate entangled commingling of meltblown fibers and other materials, e.g., wood pulp, staple fibers and particulates such as, for example, hydrocolloid (hydrogen) particulates commonly referred to as superabsorbent materials, occurs prior to collection of the meltblown fibers upon a collecting device to form a coherent web of randomly dispersed meltblown fibers and other materials such as disclosed in U.S. Pat. No. 4,100,324, to Anderson et al.
The elastic layer can be an elastic film, an elastic web, elastic fibers or any combination thereof such as, for example, an elastic web containing elastic fibers. The elastic webs can contain at least one layer of elastomeric meltblown fibers and optionally at least one layer of substantially parallel rows of elastomeric fibers. The elastomeric fibers can be in substantially parallel rows and can be autogenously bonded to at least a portion of the meltblown fibers. This bonding can take place, for example, by forming molten elastomeric fibers directly to a layer of meltblown fibers to provide the autogenous bonding.
The elastomeric fibers of the invention can have an average diameter ranging from about 40 to about 750 microns. For example, in a preferred embodiment the elastomeric fibers can have an average diameter ranging from about 100 to about 500 microns. More preferred elastomeric fibers can range from about 250 to about 350 microns and can make up at least about 20 percent, by weight, of the non-woven elastic fibrous web layer. Preferably, the non-woven elastic fibrous web layer can contain from about 20 to about 100 percent, by weight, of elastomeric fibers.
In one aspect of the present invention, the composite elastic material of the present invention can have a cup crush of less than about 120 g cm. A preferred composite elastic material of the present invention can have a cup crush of less than about 115 g cm. A more preferred composite elastic material of the present invention can have a cup crush of less than about 110 g cm. A slightly more preferred composite elastic material of the present invention can have a cup crush of less than about 100 g cm. A much more preferred composite elastic material of the present invention can have a cup crush of less than about 90 g cm. A very much more preferred composite elastic material of the present invention can have a cup crush of less than about 80 g cm. The most preferred composite elastic material of the present invention can have a cup crush of less than about 70 g cm.
In another aspect of the present invention, the composite elastic material can have a cup crush range of from about 70 g cm to about 90 g cm.
The composite elastic material of the present invention can have a density less than about 0.085 g per cubic cm. Preferably, the composite elastic material of the present invention can have a density less than about 0.075 g per cubic cm. More preferably, the composite elastic material of the present invention can have a density less than about 0.070 g per cubic cm. Most preferably, the composite elastic material of the present invention can have a density less than about 0.060 g per cubic cm.
In another aspect of the present invention, the composite elastic material can have a density range of from about 0.060 g cm3 to about 0.075 g cm3.
The composite elastic material of the present invention can have a cup crush to density ratio from about 1579 cm4 to about 950 cm4. The preferred cup crush to density ratio for the composite elastic material is from about 1500 cm4 to about 1000 m4. A more preferred cup crush to density ratio for the composite elastic material is from about 1400 cm4 to about 1100 cm4. The most preferred cup crush to density ratio for the composite elastic material is from about 1300 cm4 to about 1100 cm4.
The composite elastic material can have a CD tensile strength of greater than about 308.4 gm. The preferred CD tensile strength is of greater than about 317.5 gm. A more preferred CD tensile strength is of greater than about 340.2 gm. A slightly more preferred CD tensile strength is of greater than about 362.9 gm. A yet more preferred CD tensile strength is of greater than about 385.6 gm. A much more preferred CD tensile strength is of greater than about 408.2 gm. A very much more preferred CD tensile strength is of greater than about 430.9 gm. The most preferred CD tensile strength is of greater than about 453.6 gm.
In another aspect of the present invention, the composite elastic material can have a CD tensile strength of from about 317.5 gm lbs to about 362.9 gm.
The composite elastic material of the present invention can have a basis weight of about 75 g/m2 to about 90 g/m2. Preferably, the composite elastic material can have a basis weight of about 85 g/m2.